1. Field of the Invention
The present invention relates generally to a wafer suction pad, specifically a wafer suction pad for holding an extremely thin wafer by suction to transport it.
2. Description of Related Art
In a chamfering machine, which handles a wafer immediately after being sliced from an ingot, the wafer can be held by certain points by suction with a suction pad and transported, because the wafer is very thick.
The necessity has arisen to use the wafer for an IC card, and a planarization apparatus such as a back grinder, which grinds the reverse (opposite to the obverse, on which electronic devices are formed) of the wafer so as to make the wafer thin, processes the wafer as extremely thin as 30 .mu.m like paper. If the extremely thin wafer is held at certain points by suction in the planarization apparatus, then cracks and chips are usually generated.
In consideration of the above disadvantage, the wafer is held and transported by suction with a suction pad whose sucking face is substantially the same as the size of the wafer in the planarization apparatus of that type.
Yet, in the conventional suction pad, the suction pad must be changed every time the size of the wafer to be processed changes; hence, the working efficiency is lowered.
Japanese Patent Publication No. 2-46331 and Japanese Patent Application Laid-open No. 8-1464 disclose a worktable to hold a wafer in process by suction. In the worktable, annular grooves are formed on a face to suck the wafer, and a suction area of the air can be selected in accordance with the outer diameter of the wafer to be held. However, neither of them discloses applying the grooves to the suction pad that is provided with an arm for transportation.